Update Mockttp to fix some security warnings

Neither actually affects the server, but it's good to clean
them up anyway, and it drops a few dependencies along the way.

Author: pimterry

package-lock.json

@@ -54,7 +54,7 @@
     "lodash": "^4.17.21",
     "lookpath": "^1.2.1",
     "mime-types": "^2.1.27",
-    "mockttp": "^2.0.0",
+    "mockttp": "^2.0.1",
     "node-fetch": "^2.6.1",
     "node-forge": "^0.10.0",
     "node-gsettings-wrapper": "^0.5.0",